Week 4 - CHT Analysis on Exhaust port

Conjugate Heat Transfer

Conjugate heat transfer (CHT) analysis can accurately predict heat transfer by simultaneous solving all the relevant solid and flow field heat transfer processes, for example: conduction through solids, free and forced convection in the gases/fluids and thermal radiation.

The CHT approach has an advantage over FE thermal analyses in that wall heat transfer coefficients and their local variations on surfaces are directly calculated within the model rather than based on simplified empirical calculations. The CHT approach therefore has benefits for those applications where heat transfer is either non-uniform or difficult to calculate empirically.

y+ value

Some mature turbulence models such as k−ϵ are only valid in the area of turbulence fully developed, and do not perform well in the area close to the wall. In order to deal with the near wall region wall functions are used, which can model the near wall region. Wall functions are equations empirically derived and used to satisfy the physics in the near wall region. The first cell center needs to be placed in the log-law region to ensure the accuracy of the results. Wall functions are used to bridge the inner region between the wall and the turbulence fully developed region. When using the wall functions approach, there is no need to resolve the boundary layer causing a significant reduction of the mesh size and the computational domain!

• First grid cell needs to be 30 < y+ < 300 (If this is too low, the model is invalid. If this is too high, the wall is not properly resolved.
• Use high-Re model (Standard k−ϵ , RNG k−ϵ )

Part 1 - Base mesh

Temperature Contour

Velocity Contour

Outlet temp

Surface Heat transfer Coeffiecient

Result

Part 2 - Refined Mesh

Temperature Contour

velocity Contour

Surface Heat Transfer Ceoff Plot

Outlet Temp plot

Results